The ultimate objectives of the proposed research are to characterize the cyclic nucleotide system of cultured pulmonary endothelial cells, and to assess the possible involvement of cyclic nucleotides in the regulation of specific biochemical activities associated with these cells, i.e., (1) inactivation of bradykinin, (2) conversion of angiotensin I to angiotensin II, and (3) production of plasminogen-activator. Since cultured pulmonary endothelial cells are not presently available, initial attempts to achieve the above objectives will employ bovine aortic cells in culture and bovine pulmonary artery cells to be isolated. Attempts will also be made to obtain pulmonary capillary endothelial cells using established tissue culture techniques and an automated Cell Culture System. Subsequent biochemical studies will employ these cells to realize the overall objectives stated above.